HONG KONG—U.S. President Donald Trump’s accusations of currency manipulation appear to be reaching an audience he may not have primarily intended.

Mr. Trump vowed on the campaign trail to revive American manufacturing, in part by taking a hard line on Chinese trade practices and labeling the country a currency manipulator. Since taking office, the president has accused both China and Japan of consistently devaluing their currencies,…

Still, some smaller economies look like they are taking notice, notably Taiwan and Switzerland. The U.S. Treasury found in October that both had engaged in persistent, one-way currency intervention, essentially by buying foreign currencies like the U.S. dollar and selling their own to maintain weak exchange rates.

Analysts say the central banks of Switzerland and Taiwan are now stepping back from those activities, perhaps to avoid closer scrutiny from the Trump administration. The upshot: The Swiss franc has advanced nearly 2% against the U.S. dollar this year, while the new Taiwan dollar has surged 5.3%. Both have outperformed the euro and yen since the U.S. election in early November.

Taiwan’s central bank bought $500 million in foreign currencies in the fourth quarter, well below its quarterly average of more than $3 billion since 2012, according to Khoon Goh , head of Asia research at ANZ in Singapore, who said he suspects it is stepping back from “currency-smoothing operations.” The central bank said it doesn’t comment on currency policy.

For the first nine months of last year, the Swiss National Bank /quotes/zigman/1379668/delayedCH:SNBN+0.12%intervened heavily in currency markets to slow the franc’s rise, spending an amount roughly equivalent to its current-account surplus for the period, J.P. Morgan/quotes/zigman/272085/compositeJPM-0.76%analysts note. Over the following four months, the scale dropped to around two-thirds of the surplus.

“It’s not an entirely fanciful suggestion that the SNB might be tapering intervention in order to the guard against the risk of being cited by the U.S. Treasury as a currency manipulator,” the analysts wrote in a note.

The Swiss National Bank declined to comment.

For the U.S. to label an economy a currency manipulator under the current law, it must have a large trade surplus with the U.S. and a hefty current-account surplus and persistently intervene in the currency in one direction. As of October, no economies met all three criteria.

Recent comments from officials in South Korea, which the Treasury has flagged for its hefty trade surplus with the U.S. and its current-account surplus, suggest they’re similarly eager to avoid U.S. ire, says Govinda Finn , senior analyst at Standard Life Investments in Edinburgh. The Korean won has surged 5.2% against the dollar this year.

But any gains in the Korean and Taiwanese currencies due to U.S. political pressure may not last, he said: “On a longer-term horizon, there’s a pretty strong case to say both of those currencies can and will weaken as the authorities look to support their economies.”